What Is a Tracking Number?
A tracking number — sometimes called a tracking code or waybill number — is a unique alphanumeric string assigned to a parcel when it enters a carrier's network. It acts like a fingerprint for your shipment, allowing the carrier's systems (and you) to locate it at any point in its journey.
Every carrier formats its tracking numbers differently. Once you understand these formats, you can often identify the carrier just by looking at the number — without needing to search.
Common Tracking Number Formats by Carrier
USPS (United States Postal Service)
USPS uses several formats depending on the service type:
- 22 digits: Standard USPS tracking (e.g.,
9400 1000 0000 0000 0000 00) — used for Priority Mail, First-Class Parcels - 20 digits starting with 94: Delivery Confirmation
- 13 characters (2 letters + 8 digits + 2 letters): International registered/express mail, e.g.,
RR123456789US
The two-letter prefix in international USPS codes indicates the service type: RR = Registered, CP = Parcel Post, EE = Express Mail.
UPS
UPS tracking numbers always begin with 1Z and follow this format:
1Z [shipper ID: 6 chars] [service level: 2 digits] [package ID: 8 digits]
Example: 1Z999AA10123456784
Total length: 18 characters. The service level digits indicate speed (e.g., ground, 2-day, overnight).
FedEx
FedEx uses several formats:
- 12-digit numeric: Standard FedEx Express tracking
- 15-digit numeric: FedEx Ground
- 20-digit numeric: FedEx Ground with barcode
- 22-digit numeric starting with 96: FedEx SmartPost / FedEx Ground Economy
DHL
- DHL Express: 10-digit numeric (e.g.,
1234567890) - DHL eCommerce: Starts with GM, LX, or similar country-specific prefixes
- Deutsche Post (parent): Uses standard S10 format (see below)
Universal Postal Union (UPU) S10 Format
The S10 standard is used by postal services worldwide for international mail. The format is always:
[2-letter service code] [8 digits] [check digit] [2-letter country code]
Example: EE 12345678 9 US
Common service prefixes:
| Prefix | Service Type |
|---|---|
| RR | Registered Mail |
| EE | Express Mail (EMS) |
| CP | Airmail Parcel |
| LA–LZ | Airmail Letter/Packet |
| EA–EZ | EMS Variants |
How the Check Digit Works
Many tracking numbers include a check digit — a calculated number at the end that validates the rest of the code. Carriers use it internally to catch data entry errors. It's computed using a weighted modulo formula applied to the other digits. You don't need to calculate it yourself, but knowing it exists explains why entering a tracking number with even one wrong digit will return no results.
Quick Identification Tips
- Starts with 1Z? → UPS
- 22 digits starting with 94? → USPS domestic
- Two letters, 8 digits, check digit, two-letter country code? → International S10 postal
- Pure 10-digit number? → Likely DHL Express
- 12–15 digit number with no letters? → Likely FedEx
When in doubt, paste the tracking number into a universal tracker — it will auto-detect the carrier for you.